1. Field of the Invention
The present invention generally relates to a double-sided image forming device, and more particularly, to a double-sided image forming device, such as a copying machine, a printer, or a facsimile apparatus, having a double-side operation unit that forms an image on a sheet fed thereto, and reverses the sheet so as to cause an image to be formed on a reverse side.
2. Description of the Related Art
To begin with, a description will be given of a sheet conveying operation of a double-side operation unit included in a conventional double-sided image forming device.
FIG. 1 is an illustration outlining the double-side operation unit included in the conventional double-sided image forming device. As shown in FIG. 1, a sheet having an image formed on one side enters from a fixing unit of an image forming unit provided in a body of the image forming device into a sheet reversing unit of the double-side operation unit. The sheet is temporarily contained in a switchback conveying path 2 via a reversibly rotatable switchback roller 1. Then, the switchback roller 1 rotates reversely so as to send the sheet to a reverse roller 3. The reverse roller 3 turns the sheet by 180xc2x0 toward a horizontal conveying path (a reconveying path) 5 provided underneath. The horizontal conveying path 5 comprises a plurality of horizontal conveying rollers 4 arranged at intervals corresponding to a length of a minimum-size sheet, and transfers the sheet to a relay roller 6 provided further downstream. Then, the sheet returns to the image forming unit provided in the body of the image forming device so that an image is formed on the other side of the sheet.
Next, a description will be given of an operation of conveying a maximum-size sheet. FIG. 2A and FIG. 2B are illustrations explaining the operation of conveying a maximum-size sheet in a conventional double-side operation unit.
In the double-side operation unit shown in FIG. 2A, the switchback conveying path 2 has a length L smaller than a length LPmax of the maximum-size sheet so that the body of the image forming device occupies little space. Upon conveying the maximum-size sheet in the double-side operation unit, a rib 7 is provided as shown in FIG. 2B so as to bring a rear end of the sheet to a refuge space upward.
However, drawing out the double-side operation unit in a direction perpendicular to the direction in which the sheet is conveyed (i.e., toward the foreground of FIG. 2B), requires a space 8 occupied by the double-side operation unit as indicated by a dashed line in FIG. 2B, which is a drawback for the body of the image forming device to occupy little space (to be thinned down).
It is a general object of the present invention to provide an improved and useful double-sided image forming device in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a double-sided image forming device which can minimize a space occupied by a double-side operation unit by adopting simple structures so that the double-sided image forming device occupies little space (is thinned down).
In order to achieve the above-mentioned objects, there is provided according to the present invention a double-sided image forming device comprising a double-side operation unit including a switchback conveying path having a length smaller than a length of a maximum-size sheet, and a movable rear end guide guiding a rear end of a large-size sheet.
According to the present invention, a space occupied by the double-side operation unit upon being drawn out from a body of the double-sided image forming device can be reduced. Consequently, the double-sided image forming device occupies little space.
Additionally, the rear end guide is turnable in accordance with a drawing and a setting of the double-side operation unit. A turning angle of the rear end guide is determined by a positioning member provided on a board of the body of the double-sided image forming device and a stopper provided on a side surface of the double-side operation unit. This simple arrangement enables the double-sided image forming device to occupy little space.
Further, the turning angle of the rear end guide can be varied continuously by indefinite steps by mounting a dial member on a turning axle of the rear end guide and providing a conical stopper on the side surface of the double-side operation unit. The present arrangement eliminates variations in dimensional tolerances of components composing the double-sided image forming device so as to realize an optimal sheet conveyance in the double-sided image forming device.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.